<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>构造函数</title>
</head>
<body>
  <script>
    function newTest(fn){
      var obj={};
      obj.___proto__=fn.prototype;
      return function(){
        fn.apply(obj.arguments);
        return obj;
      }
    }
  </script>
</body>
</html>